Indexing transmissions of this kind or similar are disclosed by, for example, DE 26 08 051 A that shows a preselector, as well as by U.S. Pat. No. 2,785,242 A that shows a so-called turning arrangement. In this known construction of indexing transmissions it is necessary to provide suitable mechanical means for end position blocking. These end position blocking means have to reliably prevent the possibility of movement beyond the end positions of the tap selector or on-load tap changer that would normally lead to significant damage of the tap selector.
In addition, DE 10 39 129 A discloses a mechanical end position block in which a separate blocking disk, which is coaxially connected with a control disk for actuation of the tap selector, cooperates with a pawl that in turn can be actuated via intermediately arranged mechanical means by the control disk. This end position block is mechanically complicated and, moreover, unsuitable for blocking two mutually independently movable Maltese wheels arranged concentrically one above the other.
DE 23 39 973 A shows an arrangement in which an abutment on the Maltese cross at the appropriate instant actuates a turning arrangement or preselector by a lever system.
DE 40 09 503 C2 discloses a further development of an indexing transmission for tap selectors of tapped transformers in which two Maltese wheels concentric one above the other on a common tap selector axis are driven by a Maltese crank having an upper and a lower entrainer pin. These two entrainer pins are offset relative to one another by 180° and engage in roller slots of the respective Maltese wheel. In addition, one Maltese wheel cooperates with a turning abutment, by which a turning lever pivotal on the shaft for actuation of a turning means or preselector at a specific point of the switching sequence. The turning lever carries a blocking plate displaceable by a slot on the shaft carrying the turning lever.